Machine Type Communication (MTC) or machine-to-machine (M2M) is also referred to as time controlled smart devices or smart objects. Applications include smart grid, intelligent transportation, environmental efficiency/protection, as well as integration of wireless sensors and sensor networks with cellular networks. M2M enables novel “Smart Services” for service providers and application developers.
When a large number of MTC devices are deployed in a specific area, the network has to face increased load as well as possible surges of MTC traffic. The same area usually contains H2H, human-to-human type devices, and network resources must be allocated to different devices in an efficient manner. MTC devices should not create unnecessary overload to the network; therefore, the network scheduling efficiency and network performance requirements under MTC load need to be solved.
3GPP, 3rd Generation Partnership Project, develops specifications for third generation mobile phone systems, and also from Release 8 (Rel-8) the next generation specifications often referred to as LTE, Long Term Evolution. The 3GPP has initiated a Study Item on RAN Improvements for Machine-type Communications (RAN, Radio Access Network). One proposal is presented in the related document R2-105365, 3GPP TSG RAN WG2 #71, “Extension of Wait Time after RRC Connection Reject”.
During a RRC (Radio Resource Control) connection setup procedure a RRC Connection Reject message will be sent to the UE (User Equipment), if the eNB (Evolved Node B) cannot accept the connection request. A Wait Time is introduced to prevent many MTC devices from attempting simultaneous connection requests. This is achieved by sending different Wait Timer values to MTC devices.
MTC devices have been regarded as low priority devices. According to the 3GPP work, MTC devices should be indicated as “Delay Tolerant” devices. According to Rel-8, the wait timer range in LTE is from 1 to 16 seconds, as indicated by the four bit address space in the information element. This would lead to low wait time variation; also MTC devices could utilize much longer wait time than the seconds of Rel-8. Increasing the wait time by linear scaling—for example multiplying the value by 100—would not solve the problem of simultaneous connection requests. This may also cause problems when the network decides on one wait time T1 based on an overload wait time probability for a user equipment UE and has to choose an available value within the wait timer range that is not so close to T1. For example, if the network sets a wait timer value of T1=140 seconds, the closest value would be 100 seconds, which has the minimum delta error of Δ=140 s−100 s=40 s. This may cause inaccuracy of the wait time settings to the UE's RRC connection request. It may cause several repeat wait time messages to be sent to the UE. Thus, it may reduce the network resource usage efficiency and delay the network overload problem.